Antonio Mittica

Extraction Techniques and Analysis of Turbulence Quantities From In-Cylinder Velocity Data

In addition to the frequently used statistical ensemble-average, non-Reynolds filtering operators have long been proposed for nonstationary turbulent quantities. Several techniques for the reduction of velocity data acquired in the cylinder of internal combustion reciprocating engines have been developed by various researchers in order to separate the mean flow from the fluctuating motion, cycle by cycle, and to analyze small-scale engine turbulence by statistical methods. Therefore a thorough examination of these techniques and a detailed comparison between them would seem to be a preliminary step in attempting a general study of unconventional averaging procedures for reciprocating engine flow application. To that end, in the present work, five different cycle-resolved data reduction methods and the conventional ensemble-average were applied to the same in-cylinder velocity data, so as to review and compare them. One of the methods was developed by the authors. The data were acquired in the cylinder of a direct-injection automotive diesel engine, during induction and compression strokes, using an advanced hot-wire anemometry technique. Correlation and spectral analysis of the engine turbulence, as determined from the data with the different procedures, were also performed.

Autocorrelation and Autospectra Estimation of Reciprocating Engine Turbulence

A general method for analyzing the time-correlation and frequency-spectral structure of turbulence in IC reciprocating engines was developed and applied to the cycle-resolved turbulent velocity fluctuation and to the fluctuating motion in its more conventional sense. It is based on an alternative definition of the Eulerian temporal autocorrelation coefficient so as to reduce this to an even function solely of the separation time within specific correlation periods into which the engine cycle is divided

A New Test Bench for HWA Fluid-Dynamic Characterization of a Two-Valved In-Piston-Bowl Production Engine

A new test bench has been sup up and equipped in order to analyze the air mean motion and turbulence quantities in the combustion system of an automotive diesel engine with one helicoidal intake duct and a conical type in-piston bowl. A sophisticated HWA technique employing single- and dual-sensor probes was applied to the in-cylinder flow investigation under motored conditions. The anemometric probe was also operated as a thermometric sensor. An analytical-numerical procedure, based on the heat balance equations for both anemometric and thermometric wires, was refined and applied to compute the gas velocity from the anemometer output signal. The gas property influence, the thermometric sensor lag and the prong temperature effects were taken into account with this procedure. The in-cylinder velocity data were reduced using both a cycle-resolved approach and the conventional ensemble-averaging procedure, in order to separate the mean flow from the fluctuating motion. New results on the statistical properties of the non-stationary engine turbulence, with particular reference to its time-frequency spectral structure, were obtained at practical engine speeds, in the range of 600--3,000 rpm, and at different locations along the injector axis, one of which was very close to the cylinder-head wall.

MSW Incineration Capacity Evaluations for the Province of Turin (Northern Italy)

This paper assesses the incineration capacity requirement of the Province of Turin through a detailed analysis of the mass streams and the properties of residual Municipal Solid Waste (MSW). Historical data series were elaborated to study the trend evolution of household generation and separate collection. Residual MSW material compositions were calculated for each year over an observed period and for planned scenarios. A waste properties model was applied to calculate the residual MSW chemical composition and the LHV. The analysis allows conclusions to be drawn about the design of the planned waste-to-energy plant and to estimate the required size and technology to be used. The results show that the use of grate furnace combustor appears to be more suitable than fluidized bed.Copyright

High-pressure rotary pump performance in Multijet CR Systems

The high-pressure hydraulic circuit of the Multi-jet Common Rail (C.R.) system has thoroughly been investigated in the last few years by researchers of the automotive field. However, shortage of knowledge is still present about the high-pressure pump performance. Hydraulic-mechanical efficiency of the pump is only known as mean value and no published data are available on the Radial-jet compression volumetric efficiency. Due to the fact that part of the pumped fuel is partially expelled by the pressure-control valve and because of the presence of the oil flowing in the cooling and lubrification circuit, the determination of the compression volumetric efficiency seems to be a hard task. In the present paper a detailed description of the Radial-jet performance has been provided. The dependence of the flow rate sucked by the high-pressure pump, on speed and load has been studied and the characteristic curve of the cooling-lubricant circuit has been determined. A special procedure was designed and applied for the experimental evaluation of the fuel leakages from the pumping chambers, so as to allow the calculus of the volumetric efficiency. The actual head-capacity pump curves at different revolution speeds were plotted and compared with the electroinjector flow-requirements so as to allow the evaluation of the efficiency of the pressure-control strategy. Furthermore the pump mechanic-hydraulic efficiency dependence on head and speed was also experimentally assessed.Copyright

Shock Event Analysis, Characteristic Considerations and Conservativeness Influence in High Pressure Injection System Cavitating Flow Simulations

A comparison between conservative and nonconservative models has been carried out for evaluating the influence of conservativeness on predicting transient flows in presence of cavitation induced discontinuities inside high-pressure injection systems. Even if nonconservative models can assure satisfactory accuracy in the evaluation of the wave propagation phenomena, they introduce fictitious source terms in the discretized equations. Such terms are usually negligible, but can play a significant role when discontinuities in the flow properties occur, producing appreciable errors on the pressure wave speed estimation. An analysis based on fluid characteristics around both the rarefaction and compression wave fronts has been carried out, showing that cavitation desinence is a shock occurrence, leading to a transition from a supersonic to a subsonic flow. For a significant evaluation of conservative and nonconservative model performances a conventional pump-line-nozzle injection system was considered because the pipe flow presented interesting cases of cavitation-induced shocks. The validity of the conservative model is substantiated by the comparison between computed pressure time-histories and experimental results at two pipe locations. The Rankine-Hugoniot jump conditions have been usefully applied to the numerical results obtained by the conservative model in order to calculate the sound speed of the traveling compression waves in the presence of cavitation. A novel algorithm of general application to calculate the shock speed predicted by nonconservative models, which points out the contribution of the internal fictitious fluxes in the wrong estimation of the shock velocity, has been introduced and validated through its application to Burgers’ equation.Copyright